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Iwate Medical University Morioka 020-8505 Japan
I read with interest the article entitled "Multidetector CT of the Spine in Multiple Myeloma: Comparison with MR Imaging and Radiography" in the American Journal of Roentgenology [1].
The authors pointed out that MR imaging might not detect lesions that have evident osteolytic change on multidetector CT. However, in our experience and also according to the literature, MR imaging is sensitive, particularly to the localized bone marrow involvement that may be associated with localized bone resorption [2]. In some tumors, such as adult T-cell leukemia, bone resorption without tumor involvement may occur as a result of the secretion of parathyroid hormone—like peptide, but such a phenomenon is not usually seen in patients with multiple myeloma.
The authors did not describe the patients' history of treatment, but some, such as the patient presented in figure 3 [1], have a long history of disease and probably a history of treatment. When treatment of multiple myeloma is effective, bone marrow lesions are replaced by fatty or fibrous tissue [3], but the bone resorption often remains. In these cases, discrepancy occurs between the bone resorption seen on CT and the bone marrow involvement seen on MR imaging.
I think that such a discrepancy might have been avoided by performing CT and MR imaging before treatment only.
References
University Hospital University of Technology D-52074 Aachen, Germany
We thank Dr. Ehara for the thoughtful remarks about our article [1] and for pointing out an important fact, that multiple myeloma lesions change their appearance on MR imaging if the treatment is effective [2]. The fact that most of the patients in our study were under treatment may have led to a discrepancy between the bone resorption seen on CT or conventional radiography and the bone marrow involvement observed on MR imaging. However, even if fibrous or fatty tissue replaces a former multiple myeloma lesion, a disruption of the trabecular bone structure stays behind and, with the bone destruction, a potential risk of fracture remains. Therefore, detection of potentially unstable bone lesions is necessary in the clinical course of these patients. Even in our small patient group, one patient with a history of treatment developed a vertebral infraction during follow-up. The causative osseous lesion was initially detected on multidetector CT only.
We absolutely agree with Ehara that the combined use of CT and MR imaging is of particular value in previously untreated patients. Nevertheless, up to 20% of patients, even those in advanced stages of the disease, have normal findings on conventional radiography and MR imaging [3]. Therefore, a highly sensitive tool for the detection of lytic bone lesions is mandatory for the application of the Durie and Salmon classification [4] and the assessment of the risk of fracture. In this respect, CT proved superior to conventional radiography.
The introduction of a fast and efficient multidetector CT assessment of the skeleton, as shown in our study [1], may replace the established conventional radiographic staging in patients who have multiple myeloma. However, new MR imaging techniques, such as perfusion, may be used for prediction of vertebral fracture risk [5]. So far, MR imaging is considered the imaging modality of choice for visualization of therapy response in multiple myeloma, and it allows determination of the prognosis [6].
Therefore, we believe that CT and MR imaging are currently complementary imaging modalities. In our opinion, the combined use of the techniques, especially for the initial staging, may add to the diagnosis.
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